1. Field of the Invention
The present invention is broadly concerned with one-time, one-use sensor assemblies designed to determine the occurrence of predetermined conditions, such as temperature values. More particularly, the invention is concerned with such assemblies and methods making use of specially designed, elongated, resilient sensor elements (preferably amorphous or nanocrystalline metal alloy glass-coated microwires). A separate detector includes a transmitter unit operable to transmit interrogating electromagnetic radiation (preferably an alternating magnetic field) to the sensor elements, and changes in the induced responses of the sensor elements indicate occurrence of the predetermined condition.
2. Description of the Prior Art
A number of one-time sensor devices have been developed in the past for use in monitoring and detecting predetermined conditions, such as temperature changes, the impact of chemical or biological agents, radiation exposure, electromagnetic fields, and structural stresses. For example, U.S. Pat. No. 6,837,620 discloses a sensor element formed of shape memory alloy, which changes shape when exposed, even temporarily, to temperatures below a predetermined critical temperature. The shape change of the element causes the sensor to change between two readily distinguishable states, such as a color change in the sensor device. However, this sensor requires a rather complicated mechanical arrangement, and has a relatively large size.
Another example of a one-time sensor device is a radiation badge indicating a cumulative ionizing radiation dose experienced by the wearer. As ionizing radiation is experienced, a film forming a part of the badge absorbs such radiation. This film, when developed, indicates the cumulative radiation dose by its blackness grade. While being reliable, the reading process is time-consuming and inconvenient.
U.S. Pat. No. 6,666,821 describes an implantable sensor system with a sensor including a protective member preventing the sensor from interacting with the surrounding environment. At a selected time, the protective member is disabled by application of an electrical potential serving to dissolve the member. In another embodiment, the protective member dissolves within a body over a predetermined time period.
U.S. Pat. No. 7,689,260 describes an extended use, slowly implantable microwire electrode, which is coated with temperature-sensitive shape memory polymer. A drawback of these sensors is the need to directly couple the microwire electrode to electrical leads, making it impossible to wirelessly communicate with the electrode. A similar type of implantable device is described in U.S. Pat. No. 5,653,742.
U.S. Patent Publications 2008/0175753 and 2010/0006562 describe glass-coated microwire sensors designed for wireless communication by means of an alternating magnetic field detector. These devices are not single use sensors. There is accordingly a need in the art for a relatively inexpensive, one-time sensor unit operable to indicate the occurrence of a predetermined event, such as temperature or the like.